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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Foodborne Toxin Detection and Prevention Research » Research » Publications at this Location » Publication #397266

Title: T-cell-receptor Vß8 for detection of biologically active streptococcal pyrogenic exotoxin type C

item Rasooly, Reuven
item Do, Paula
item Hernlem, Bradley - Brad

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2023
Publication Date: 10/4/2023
Citation: Rasooly, R., Do, P.M., Hernlem, B.J. 2023. T-cell-receptor Vß8 for detection of biologically active streptococcal pyrogenic exotoxin type C. Journal of Dairy Science. 106(10):672-6730.

Interpretive Summary: One cause of food poisoning is the bacteria Streptococcus pyogenes, a germ more often spread through droplets in the air but also in contaminated foods including milk and milk products. Beside infection, it also makes 13 different toxins that affect consumer health. We are the first to demonstrate that one of these toxins, SPE-C activates T-cells expressing receptor Vß8. We utilized this finding in developing a method to detect rSPE-C, using engineered human cells that make light and a chemical, IL-2, when active rSPE-C is present. Light is produced in as little as 5 hours and the amount doubles by 24 hours. We added rSPE-C to milk and tested whether heat treatment (pasteurization) could reduce the toxin’s activity. We found that rSPE-C was heat stable in milk but not in buffer. This means that heat treatment of food to kill the bacterium will not necessarily eliminate the toxin.

Technical Abstract: Streptococcus pyogenes is an important human pathogen, commonly spread by airborne droplets but also by ingestion of contaminated food. Apart from causing infection, this pathogen produces 13 distinct types of streptococcal pyrogenic exotoxins (SPEs). The current method for detection cannot distinguish between the biologically active form of SPEs that has been reported to cause foodborne outbreaks and the inactivated toxin which poses no health risk. To measure the biological activity of SPE-C, one such toxin that was linked to foodborne outbreaks associated with milk and milk products, we developed a cell-based assay that can discern between biologically active and inactive SPE-C. We are the first to demonstrate that SPE-C activates T-cells expressing Vß8 and with this finding used a genetically engineered T-cell line natively expressing Vß8 and with the luciferase reporter gene under the regulation of nuclear factor of activated T-cells response element (NFAT-RE) combined with a B-cell line to present the rSPE-C-MHC class II to the Vß8 TCR in an assay to detect and to discern between biologically active and inactive rSPE-C. By using this system, we demonstrated that rSPE-C induced significant IL-2 secretion 72 hours and visible light emission after only 5 hours, doubling by 24 hours. We utilize this finding to assess the specificity of the assay and the effect of pasteurization on rSPE-C activity. We observed no cross reactivity with SPE-B and significant loss of rSPE-C biologically activity in spiked PBS but in spiked milk rSPE-C is heat stable and heat treatment did not reduce its biological activity. Once rSPE-C has formed, it is infeasible to eliminate it from milk by thermal treatment.